(1) Field of the Invention
The present invention relates generally to label systems and, more particularly, to a heat-activated label system for transferring a preprinted label and a protective coating in a single step from label stock to a substrate, such as a plastic crate or glass bottle.
(2) Description of the Prior Art
Containers, such as glass bottles, are currently labeled in several different ways. The predominant method is printed paper labels glued to the container at the time of filling and sealing. Such labels offer almost unlimited art potential and are commonly used on food and both returnable and non-returnable beverage containers. This is the lowest cost technique, but offers little resistance to label damage. Also, the glue systems used are a constant source of problems in high speed bottle filling operations.
A second, more recently developed, container labeling technique is of applying a thin styrofoam label to cover the container from shoulder to heel, with the decorative and/or informational material being printed on the more dense outer skin of the styrofoam label. This is widely used on lighter-weight, one-way bottles common in the beverage industry. It offers some impact resistance and a large surface area for printing product information and instructions, as well as company logos. Unfortunately, it covers a majority of the container and prevents visual inspection of the contents by the consumer. In addition, it is more costly than the paper label, has little durability and becomes easily soiled. Also, because the printing surface is relatively rough, high definition printing is not possible. The styrofoam label also becomes a contaminate at the glass recycling center as well as at the glass plant when remelting the container.
A third container labeling technique is printing ceramic ink directly on the container surface using a screen printing technology. While the label appearance is generally good, the technique is typically limited to two or three colors due to cost considerations. A recent development is the preprinting of a ceramic ink decal which is then transferred to the glass container surface. This permits high definition printing and offers greater opportunities for color and art variety. Fired ceramic inks are extremely durable and will survive the alkali washing processes required of a returnable container. However, both the direct printing ceramic ink and ceramic ink decal techniques require subsequent high cost, high temperature firing to fuse the ink to the glass substrate. In addition, while the preprinted ceramic ink label reduces the technical problems somewhat, both techniques require extreme attention to detail and a high level of maintenance and are run off-line at slower speeds, with high labor costs. Due to these higher costs, ceramic inks are the least commonly used labeling technique.
Another, more recent, technique is disclosed in U.S. Pat. No. 5,366,251, issued to Brandt. Brandt teaches a label comprising an opaque or clear film substrate, which has preferably been coated on both sides with acrylic to serve as a compatible interface bond with the other materials used in the process and also to provide a high gloss surface. Graphics are printed on the acrylic layer, preferably using a solvent-based acrylic ink. The graphics can be reverse printed when the film is clear, which gives the appearance of the xe2x80x9cfired onxe2x80x9d label. When the film is opaque, the graphics are front surface printed using the opaque film as a background or part of the graphics. The label is then provided on its container side with a two-layer, heat-activatable adhesive, activatable on contact with the heated container. A clear coat may be subsequently applied to protect the label during use, however, this requires a separate step.
U.S. Pat. Nos. 5,650,028 and 5,458,714, also issued to Brandt, disclose other embodiments of this technique and machinery to carry out the application of the label to the container. All three of these patents are hereby incorporated by reference in their entirety.
These techniques have also been considered for applying replaceable labels to polyethylene beer crates. However, the label must be sufficiently durable to pass scuff and water-soak resistance tests while, at the same time, be removable by a weak caustic solution to enable a new label to be added. Because the label must be easily removed, the label can not use a conventional protective, clear coat to provide the necessary protection to the label.
Thus, there remains a need for a new and improved heat-activated label system for transferring a preprinted label and a protective, clear coat in a single step from the label stock to a substrate, such as a plastic crate or glass bottle while, at the same time, selectively providing removability for crates or permanence for bottles and with improved scuff and water-soak resistance.
The present invention is directed to a label system having an unique label stock. The label stock includes a water-reducible ink system for forming a water resistant ink label. In the preferred embodiment, the ink system includes a color coat layer comprised of a first carboxylic acid functional resin selected from the group consisting of urethane, epoxy and acrylic carboxylic acid functional resins; and a protective, clear coat layer including a second carboxylic acid functional resin. For bottle applications, hydrophobic fumed silica was added to improve scuff and water resistance in the parent invention. A label carrier, formed from non-absorbent paper or plastic, receives the water resistant ink label.
The protective, clear coat layer is located between the surface of the label carrier and the color coat layer but becomes the outer layer of the label when the label is transferred to a substrate, such as a bottle or plastic carton. In the preferred embodiment, a silicon release finish is added between the protective, clear coat layer and the label carrier to aid in the release of the label from the label carrier surface. Also, a conventional, clear release coating may be added between the release finish and the label to provide additional protection for the label after transfer. As used herein, a release finish substantially stays with the label carrier and a release coating transfers with the label to the substrate.
In the preferred embodiment, a heat-activated adhesive is applied to the surface of the color coat layer for transferring the label from the label carrier to the substrate. The heat-activated adhesive has an activation temperature that is less than the distortion temperature of the label carrier, so as to not distort the image during transfer. Preferably, the activation temperature of the heat-activated adhesive is less than about 350xc2x0 F. and, most preferably, is about 150xc2x0 F.
In the preferred embodiment of the parent invention, the heat-activated adhesive was an acrylic emulsion system which includes an adhesive agent, an anti-tacking agent, a viscosity stabilizer, and with the balance being water and further may include a plasticizer and a wetting agent to reduce xe2x80x9cspider webbingxe2x80x9d in some applications.
In the present invention, a polyurethane dispersion system has been developed for use in addition to the acrylic emulsion system of the parent invention. It has been found that the polyurethane dispersion system of the present invention produces superior performance over the acrylic emulsion system for high scuff-resistant cases, such as bottles where more resistance is needed, while, at the same time, eliminating the need for fumed silica to be added.
Also, in the preferred embodiment, the label stock further includes an intermediate, clear, primer coat between the adhesive and the water resistant ink label which provides improved transfer of the label from the label carrier to the substrate. In addition, it has been discovered that the use of the intermediate, clear, primer coat also improves removability for crate applications over just ink alone. Apparently, the inks become resoluble more quickly than the clear primer coat does.
Finally, a heat-activated, cross-linking agent may be added in at least one of the color coat, the protective, clear coat or the heat-activated adhesive to improve water-soak resistance for bottles or other applications where the label is not removable. The heat-activated, cross-linking agent is preferably selected from the group consisting of urea and melamine formaldehyde. The heat-activated, cross-linking agent has an activation temperature that is greater than the activation temperature of the adhesive and preferably is greater than about 250xc2x0 F. In the most preferred embodiment, the heat-activated, cross-linking agent has an activation temperature of about 380xc2x0 F. This allows the adhesive to be activated at a first, lower temperature and the cross-linking agent to be activated at a second, higher temperature after the label has been transferred to the substrate. However, because of the mechanics of transferring a label, the heat-activated, cross-linking agent may have an activation temperature as low as about equal to the activation temperature of the adhesive and still perform satisfactorily.
Accordingly, one aspect of the present invention is to provide a label stock including: (a) a water-reducible ink system for forming a water resistant ink label; (b) a label carrier having a top surface and a bottom surface for receiving the water resistant ink label on said top surface; and a heat-activated adhesive for transferring the label from the label carrier to a substrate, wherein the heat-activated adhesive is a polyurethane dispersion system.
Another aspect of the present invention is to provide a water-reducible ink system, the system including: (a) a color coat layer comprised of a first carboxylic acid functional resin; and (b) a protective, clear coat layer, wherein the protective, clear coat layer includes a second carboxylic acid functional resin and with the balance being water.
Still another aspect of the present invention is to provide a label stock, including: (a) a water-reducible ink system for forming a water resistant ink label, the system comprising: (i) a color coat layer comprised of a first carboxylic acid functional resin; and (ii) a protective, clear coat layer, wherein the protective, clear coat layer includes a second carboxylic acid functional resin and with the balance being water; (b) a label carrier having a top surface and a bottom surface for receiving the water resistant ink label on said top surface; and (c) a heat-activated polyurethane dispersion adhesive for transferring the label from the label carrier to a substrate.
These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment when considered with the drawings.